The present invention relates to a phenolic molding composition used in engine parts or the like mounted on a vehicle, and more particularly relates to a phenolic molding composition improved in wear resistance, especially in abrasive wear resistance, and a pulley molded of the composition.
Since phenolic molding compositions are superior in heat resistance and dimensional stability, they have been used as alternative materials to metal parts in various fields. In the field of vehicles, making various parts out of resin has been promoted with the increase in demand for reduction in size, weight and cost. Particularly, pulleys which have been heretofore chiefly made of metal are being replaced by those made of resin. Such resin pulleys have been molded with various shapes.
However, particularly in the case of a pulley made of phenolic resin, the contact surface of the pulley with a rubber belt is apt to wear out if the pulley is used in the state where dust is nipped between the pulley and the belt. Thus, there is a disadvantage that the resin pulley is inferior in durability compared to the general metal pulley. In order to prevent such dust from entering, An attempt on covering of the whole of an auxiliary driving portion of an engine with a cover is therefore considered. Such an attempt is, however, impractical because it is against the demand for reduction in weight and cost. Therefore, it is essential to improve the wear resistance, particularly the abrasive wear resistance of the pulley itself.
The pulley made of phenolic resin is easily cracked because of a difference in thermal expansion coefficient from a metal insert in the environment in which variations in temperature are violent. Therefore, there is a problem that the pulley is inferior in heat shock resistance.
Therefore, a resin pulley made of phenolic resin mixed with inorganic fiber, inorganic powder, organic fiber and elastomer has been proposed, for example, as described in Japanese Patent Laid-Open No. 217818/1997. Fine silica powder with an average particle diameter of 10 xcexcm is used as the inorganic powder in such a resin pulley. In this case, there is a problem that the abrasive wear resistance is insufficient so that the abrasion loss of the pulley increases. Thus, further improvement has been demanded.
Taking the problems in the related art into consideration, the present inventors have made various researches. As a result, the present inventors have found that a molded product, particularly a pulley, is improved in wear resistance and heat shock resistance by compounding, in a phenolic resin molding composition, resol-based phenolic resin, inorganic fiber, silica powder with an average particle diameter of from 20 to 150 xcexcm, and a rubber component in specific proportions. Thus, the invention has been accomplished.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A phenolic molding composition comprising;
a resol-based phenolic resin; and
40 to 100 parts by weight of inorganic fiber;
30 to 90 parts by weight of natural silica powder with an average particle diameter of from 20 to 150 xcexcm; and
1 to 15 parts by weight of a rubber component, each per 100 parts by weight of the resol-based phenolic resin.
(2) The phenolic molding composition according to (1), wherein the inorganic fiber includes 50% or more by weight of glass fiber.
(3) The phenolic molding composition according to (1) or (2), wherein the natural silica powder is shaped like pulverized powder.
(4) The resin pulley molded of a phenolic molding composition defined in any one of (1) to (3).
A phenolic molding composition for forming a pulley according to the invention will be described below in detail.
A resol-based phenolic resin used in this invention may be dimethylene-ether-based or methylol-based and either of a solid type or of a liquid type. Especially, a solid type phenolic resin with an average molecular weight of from 600 to 800 may be used preferably in order to improve heat shock resistance. The resol-based phenolic resin has a function of uniformly dispersing a rubber component mixed as a stress absorber in this invention, further has a function of reducing molding pressure at the time of injection molding to reduce stress remaining in the pulley. Accordingly, the resol-based phenolic resin improves heat shock resistance.
In order to improve abrasive wear resistance which is an object of this invention, it is essential to increase hardness of additives and surface hardness of the composition and to reduce elastic modulus. From this point of view, a rubber component, inorganic fiber and silica powder are compounded in the molding composition according to this invention.
The rubber component used in this invention is not particularly limited but nitrile rubber, acrylic rubber, polychloroprene rubber, styrene-butadience rubber, silicone rubber or the like may be used preferably. One selected from these rubber components maybe used singly or two or more rubber components may be used in combination. Preferably, 1 to 15 parts by weight of the rubber component are contained in 100 parts by weight of phenolic resin. If the amount of the rubber component is smaller than 1 part by weight, the effect for reduction in elastic modulus cannot be exhibited. If the amount of the rubber component is larger than 15 parts by weight, the effect for reduction in elastic modulus can be obtained but improvement in abrasive wear resistance cannot be obtained because of extreme reduction in surface hardness and strength.
As the inorganic fiber used in this invention, it is possible to use glass fiber, carbon fiber, silicon carbide fiber, potassium titanate fiber or the like. One selected is from these materials maybe used singly or two or more materials may be used in combination. Especially, inorganic fiber containing not smaller than 50% by weight of glass fiber may be used preferably from the point of view of strength, heat resistance, cost, and soon. The glass fiber maybe preferably subjected to a surface treatment with a silane coupling agent in order to improve adhesion to the phenolic resin.
In this invention, 40 to 100 parts by weight of the inorganic fiber is contained in 100 parts by weight of the phenolic resin. If the amount of the inorganic fiber is smaller than 40 parts by weight, the reinforcing effect is poor in practical use of the pulley. If the amount of the inorganic fiber is larger than 100 parts by weight, the characteristic of attacking the rubber belt becomes high as well as the abrasive wear resistance becomes low because of increase in elastic modulus. Therefore, it is undesirable to determine the amount of the inorganic fiber which is smaller than 40 parts by weight or is larger than 100 parts by weight.
In this invention, natural silica powder with an average particle diameter of from 20 to 150 xcexcm is used. In accordance with crystalline state, natural silica is classified into crystal silica and amorphous molten silica. Either of them maybe used. The shape of natural silica powder is classified into a pulverized type and a round grain type. Especially, the pulverized type natural silica powder may be preferably used because the frictional resistance due to mobility of the pulley prevents the silica powder from dropping out. If the average particle diameter of the natural silica powder is smaller than 20 xcexcm, the contact surface area of the particles with the phenolic resin becomes small so that the particles are apt to drop out undesirably. If the average particle diameter is larger than 150 xcexcm, the surface of the finished product is roughened so easily that the abrasive wear resistance becomes low undesirably.
Preferably, 30 to 90 parts by weight of the natural silica powder are contained in 100 parts by weight of the phenolic resin. If the amount of the natural silica powder is smaller than 30 parts by weight, a sufficient effect cannot be given to wear resistance because of shortage of the proportion of the silica powder on the surface of the pulley. If the amount of the silica powder is larger than 90 parts by weight, the adhesion between the phenolic resin and the silica powder is lowered because of relative reduction in the amount of resin so that the silica powder is apt to drop out of the surface of the pulley.
Various kinds of additives commonly used in the general phenolic molding composition, for example, releasants such as calcium stearate, accelerators such as magnesium oxide, anti-oxidants such as hindered phenol, light stabilizers such as hindered amine, ultraviolet light absorbers such as benzotriazole, and colorants, may be added to the molding composition according to the invention as occasion demands.
Further, organic fiber such as cotton cloth fiber, aramid fiber or the like can be added to the molding composition according to the invention if the organic fiber does not disturb the object of the invention.
The molding composition according to the invention can be produced by heating and kneading in a press kneader, a biaxial extruder, a Henschel mixer, a mixing heat roll or the like and by pulverizing in a power mill or the like. In addition, a pulley having a desired shape can be molded by a known molding method such as an injection molding method, a transfer molding method or a compression molding method.